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Context for the questions:

I am building my first real guitar soon. I have previously built a semi-decent ukulele which plays well, and other random stringed instruments. I’ve been woodworking for a few years, and also playing guitar for around the same amount of time. I decided to marry those two passions and build a guitar. I am building a telecaster style guitar with a P90 in the neck. I am routing and fabricating the body, and wiring the electronics myself. I bought a neck premade. I hope to in the future build my own neck, but for this first build I wanted to eliminate as many things that could go wrong as possible. I have all of the tools and routing jigs to make this thing at least halfway decent. I’ve planned it all out except for one last little bit: the finishing of the body.
I have a relatively inexpensive HVLP spray gun I got a year ago for finishing my furniture projects. It has made finishing a breeze. I’ve almost exclusively used oil based polyurethane with the gun. At its finest setting it gives a bit of a bumpy texture to whatever I’m spraying. I really like the texture, and in all honesty, for a first guitar, I wouldn’t mind a textured finish. I plan on buying a real fancy HVLP spray gun and an air compressor at some point, but not anytime soon. I want to stick with this gun for the build, and I believe it’s good enough.
My original plan was to make the body out of hard maple (yes, I know it is unorthodox and will be insanely heavy) and dye the body and headstock a nice turquoise blue. This original plan had a few flaws. First, the water based dye would be a pain as it would raise the maple grain. Second, hard maple would be annoyingly hard to route and sand. Third, the type of polyurethane I planned on using was the Behr brand, which I do not believe is instrument grade.
I then remembered lacquer is a finish too, and I got really excited. I got even more excited to find out that it could be tinted. If I use some I plan on going with Mohawk instrument nitrocellulose lacquer.

Now finally, here are the questions:

I’ve never sprayed lacquer out of my HVLP spray gun. I know that lacquer works by softening the layer under it to adhere. Do I have a better chance at getting a smoother finish with the gun if I use it? I obviously will practice with the gun before using it on the guitar. Does it spray relatively similarly to polyurethane? Should I not even try with lacquer, and just stick with polyurethane?
I want to do an opaque tint. Which products will give me that property? How much would I need to mix it? If I spray opaque lacquer, should I do a few coats of opaque and then a final few top coats of clear? Are there any big things I need to keep in mind or be weary of? Do I need to do some end grain filling if I use a relatively closed-pore wood like alder?
To smooth the body a bit after finishing, what do y’all recommend in terms of buffing? I don’t have a large buffer, but I do have a 5” random orbit sander and a 6” angle grinder. Which compounds do I need for that? Ideally I’d like to do a satin finish if possible. Should I even spray the headstock? Will it be really hard to keep the lacquer from bleeding over to the side of the headstock? I consider myself generally good at masking.

You have many questions with overlapping thoughts. If you want a satin finish, there is no buffing. Decide gloss/satin first. Nitro is much easier IMO than any other finish. If your poly is bumpy; you may not be thinning it enough. A cheap hvlp gun can do a decent job of spraying a guitar as a more expensive one (within limits). It is more technique than gun IMO.

Lacquer spraying needs a non-explosive well ventilated environment (maybe outdoors) and a good facial ventilator. That's one advantage of the other types of finish, although I use a ventilator with those too. As to dyes, I find that thinning with alcohol does not raise the grain and with maple (I've only used figured maple) you can sand it back to highlight the grain pattern. Maybe use several sand backs or colors to really make it pop. You can also add the dye to the first few clear coats to tint it then clear coats over the top. Anyway, PRACTICE ON SCRAP! and have fun.

I don’t spray, so I am no help. I just wanted to ask why you are planning to use hard maple if you want an opaque finish? You could use any wood you want. If you want turquoise hard maple look you can do that with lacquer by spraying translucent coats to the color/concentration you want and switch to clear after that.

Also, if you want hard maple but are worried about the weight and routing, you could put a thinner cap of maple over a lighter wood so that the top 1/4” or so is maple and the rest is something else. If you were planning on doing an arm bevel, that would need to be taken into consideration. Heck, you could even bender the top.

_________________
Bryan Bear PMoMC

Take care of your feet, and your feet will take care of you.

I planned on using maple only if I was to do a dye. I would use alder if I went for an opaque finish. I wanted to do a maple body so that the dye on the headstock would match the dye on the body if I went with it.

Jacob, as Glen said, you have asked about every question there is about finishing, Let me make a coupe of comments but you need to keep the context. I have built close to 30 guitars now, finished most of them in traditional nitrocellulose lacquer. I have experimented with some of the water born lacquers, keep coming back to nitro. I have not shot any of the modern poly finishes so I have no perspective.

I most do transparent finishes but I do use stains on bare wood and I do mix dyes into my lacquer to change color. I have made several guitars with maple caps (never solid) and have used stains to pop the figure of highly figured wood. Maple is stunning wood and you can do some really fun stuff with it.

I spray with a small inexpensive HPLV gun and small home compressor. I do not have a real spray booth but I am very aware of both ventilation and safety. Nitro is a really nice finish for a relative beginner because of the way each coat melts into the previous ones - you can sand out sags and shoot another coat without the worry of witness lines. Nitro seems to take dyes well to make transparent colors, I have not done any solid opaque finishes (those use pigments for their color). I do most of my staining with transtint dyes dissolved in DNA - I like the results better than water but there are reasons for both.

Dan Erlewine's book on guitar finishing is a good reference. It is a bit dated because he does not talk about all the modern catalyzed finishes, but for nitro and water born lacquer its pretty good. One of the cardinal rules of finishing is to always experiment on scraps of the same wood and to do all of the steps so you can see how different layers interact.

I would also recommend the finishing sub forum at TDPRI.com mainly because its fairly active and has quite a few people at about your level of experience